Synthetic detergents, such as cationic, anionic, amphoteric, non-ionic surfactants, are widely used in personal care cleaning compositions. Anionic surfactants generally exhibit superior cleansing and foaming properties and are thus typically incorporated into such compositions. Anionic surfactants, however, also tend to be harsh on the skin.
Since consumers desire milder compositions (i.e., compositions which are not as harsh and irritating on skin and skin proteins), it is known to replace some anionic surfactant with other surfactants (e.g., nonionic and/or amphoteric surfactants). Another approach is to associate anionic surfactants with amphoteric or cationic compounds to create surfactant complexes (see U.S. Pat. No. 4,443,362). Often these compositions suffer in foaming and/or cleansing performance.
Another approach for providing mildness is to use milder anionic surfactants. Among such mild anionic surfactants that can be used are N-acylamino acids and their salts.
The paper “Surface Active N-Acylglutamate: Preparation of Long Chain N-Acylglutamic Acid” (M. Takehaka et al.; Journal of the American Oil Chemists Society, Vol. 49, p. 157 ff) cites JP Patent No. 29444 (1964) according to which acyl glutamates are said to alleviate skin irritations caused by other anionic surfactants such as alkylbenzene sulfonates.
As seen in U.S. Pat. No. 6,703,427 to Schmucker et al., such acylamino acids are contemplated as co-surfactants to alleviate harshness of primary anionic surfactants. By themselves, as the primary surfactant (a “primary surfactant” is one which is present at a level of 50% or more of all surfactant) in a surfactant cleansing system (as is preferred for compositions of the invention), or as the primary anionic surfactant (as a “primary anionic surfactant”, the surfactant is present at 50% of all anionic surfactants; however, surfactants other than anionic surfactants may in total comprise greater than 50% of the entire surfactant system or less than 50% of the system), such surfactant would be expected to be deficient in foam and/or cleansing relative to use of other anionic surfactants in the same composition. Further, acylamino acids are difficult to solubilize at lower pH ranges because the molecule will tend to precipitate. It would generally not be contemplated thus to use acylamino acids such as glutamate at a low pH and, typically, salt of glutamate does precipitate at about a pH of 5.5 and lower. As such, such glutamate salt molecules would not be contemplated for use in isotropic liquids (where solubility is required to ensure good clarity) at any significant level. In particular, they would not be contemplated for use as primary surfactant, or as a primary anionic surfactant and where, simultaneously, the amount of glutamate is equal to or greater than, preferably greater than, any other single surfactant present. That is, according to our invention, if the salt of glutamate is primary anionic surfactant but the total sum of non-anionic surfactants is greater than that of anionic surfactant, the salt of glutamate must be present in an amount equal to or greater than any other surfactant present. It is preferred that the glutamate salt be present as the primary surfactant.
It would further not be contemplated to use acyl glutamate (unless specified otherwise, we use term “glutamate” or “acyl glutamate” to mean the salt of the glutamate) as a primary surfactant or as a primary anionic surfactant (where glutamate is simultaneously present in an amount equal to or greater than any other single surfactant present), because glutamate does not structure (e.g., self-structure) as readily as other surfactants and therefore can make it more difficult to suspend particles and other benefit agents. Further, it is not readily apparent how to structure with external structurants while maintaining a relatively clear, isotropic liquid, particularly at a low pH (e.g., of 6.5 and lower, preferably 6.0 and lower). The subject application relates to compositions where glutamate is the primary surfactant (and by definition the primary anionic surfactant) and in which specific structuring polymers are used to provide good structuring (defined by initial bulk viscosity) and stability (defined by viscosity and clarity maintenance and no phase separation) of the liquids while maintaining desired clarity (at low pH of 6.5 and lower, preferably of 6.0 and lower, more preferably of 4.0 to 5.1).
In short, because acyl glutamate surfactants are not the type of anionic surfactants which provide superior foaming, because they do not readily solubilize (at lower pH), and because they do not self-structure as well as other anionics, such surfactants would not have been considered for use in a low pH (pH of 6.5 and lower) liquid cleansing composition as the primary surfactant; or as primary anionic surfactant, but where the amount of glutamate is present in amounts equal to or greater than any other single surfactant present. In particular, they would not be contemplated for use as primary or primary anionic surfactant in aqueous-based cleansing compositions while retaining the ability to maintain good structure, stability and clarity.
Unexpectedly, applicants have found that it is possible to formulate low pH, aqueous-based isotropic compositions (which are structured, stable and clear) in which acyl glutamate is primary surfactant (preferred systems); or primary anionic surfactant and simultaneously present in an amount equal to or greater than any other single surfactant present. According to the subject invention specific structuring polymers are used. Preferably, the pH of the composition is 6.5 and lower. More preferably, of pH is 3.5 to 6.0. More preferably, pH is 3.5 to 5.5 and most preferably 4.0 to 5.5, even more preferably 4.0 to 5.1. Preferably, the composition is visibly clear (isotropic). Preferably, the composition is a single phase (single phase which is isotropic), clear composition where clarity is defined by an absorbance value of 1.0 or lower, preferably 0.5 or lower (e.g., 0.01-0.5), more preferably 0.2 and below when measured at wavelength of 550 nm. Use of specific structuring polymers permits clarity to be maintained while maintaining good structure (i.e., initial bulk viscosity) and stability (i.e., viscosity and clarity maintenance under defined conditions and no phase separation under defined conditions).
Further, applicants have found that, when the amount of shorter chain glutamate (as a percent of all glutamate) is minimized (to ensure good foam) and the percent of glutamate relative to co-surfactant is maximized (saving on cost of use of co-surfactant while surprisingly maintaining low pH, clear, one phase isotropic compositions), preferred compositions are found. In preferred systems, glutamate is the primary surfactant (present at level of 50% or more, preferably 55% or more of all surfactant). Preferred systems comprising glutamate and particular co-surfactants are also disclosed.
In the subject application, applicants disclose compositions in which specific polymers can be used to ensure structured, stable, isotropic liquids which are formed at relatively low pH (of pH 6.5 and lower, preferably pH of 6.0 and lower, preferably pH of 5.5 and lower) while also maintaining defined level of clarity. As noted, these compositions are stable as defined in at least two ways. They are stably structured in that, using structurants of the invention, they have initial bulk viscosity of at least 1000 cps, and they are stable in that compositions maintain viscosity and clarity and do not separate under defined conditions. Such structured, stable and clear compositions would not be expected to form in systems where glutamate is the primary surfactant, or the primary anionic surfactant while simultaneously present in an amount equal to or greater than any other single surfactant present.
As noted, stability is defined in part to include maintenance of clarity. Thus, when we define compositions as structured, stable and clear, this is simply to emphasize the importance of both clarity initially and over time.
A variety of compositions have been disclosed where glutamate is disclosed broadly.
In U.S. Pat. No. 6,284,230 to Sako et al. a broad number of surfactants, including glutamates are said broadly to be able to be used as primary anionic surfactant. From the examples however, it is clear that where glutamate is used (Examples I-V), it is neither the primary surfactant (ammonium sulfate is in Examples I-V) nor is it the primary anionic surfactant. In Example VI, sarcosinate (different acyl amino acid with a single carboxylic acid group) is the primary surfactant. Never is an acyl amino acid having two carboxylic acid groups (such as glutamate) used as primary surfactant or as primary anionic surfactant in which the glutamate is used in an amount equal to or greater than any other single surfactant present.
US 2004/0258807 and US 2011/016506 are two other examples of references disclosing glutamates broadly but again it is clear that glutamates are never used as primary surfactants; or as primary anionic surfactant and where glutamate is simultaneously present in an amount equal to or greater than any other single surfactant present in the composition.
US 2005/034895 shampoo compositions comprise surfactant, microbiological control agent, rheological additive, conditioning agent and solubilizer. The surfactant compositions include mixtures of glutamate and other surfactants (see Examples 2-5), but glutamate is never primary surfactant or primary anionic where it is used in amounts equal to or greater than any other single surfactant in the composition.
WO 2010/069500 discloses in Example 1, Composition E, a composition having 3.5% glutamate, 3.5% sarcosinate, 8.5% betaine and 2.5% glucoside. In this composition glutamate is primary anionic (is present at level of 50% of anionic), but is not present in an amount equal to or greater than any other single surfactant present (e.g., betaine is single greatest surfactant present). It is also not the primary surfactant.
The present invention, as noted, requires the glutamate be either primary surfactant (preferred embodiment); or present as primary anionic surfactant while simultaneously being used in an amount equal to or greater than, preferably greater than, any other single surfactant present in the composition. For reasons noted above, formation of such system would not be contemplated because such systems where glutamate is used (especially as primary surfactant) in such relatively large amounts would have been thought to compromise the formation of compositions which are clear (isotropic), foam well, are well structured (i.e., defined by initial bulk viscosity) and are stable (defined by both viscosity and clarity maintenance as well as by absence of visible phase separation). Further it was unexpected that specific structuring polymers work so well to ensure structure and stability of the composition while also maintaining low pH, clear, isotropic composition (clarity maintenance as noted being encompassed by definition of stability).